Step seal for refrigerant compressors

ABSTRACT

In some aspects, the techniques described herein relate to a refrigerant compressor, including: a stator; a rotor configured to rotate with respect to the stator; and at least one step seal between the rotor and the stator, wherein the step seal includes a first tooth and a second tooth extending from the rotor toward the stator, wherein a downstream surface of the first tooth and an upstream surface of the second tooth are arranged at an angle relative to one another, wherein the angle is less than 90°.

RELATED APPLICATIONS

This application is a continuation of prior U.S. application Ser. No.17/546,161, filed Dec. 9, 2021, the entirety of which is hereinincorporated by reference. The '161 Application claims the benefit ofU.S. Provisional Application No. 63/133,471, filed Jan. 4, 2021, andalso claims the benefit of U.S. Provisional Application No. 63/224,479,filed Jul. 22, 2021. The entirety of the '471 and '479 Applications areherein incorporated by reference.

BACKGROUND

Refrigerant compressors are used to circulate refrigerant in a chillervia a refrigerant loop. Refrigerant loops are known to include acondenser, an expansion device, and an evaporator. The compressorcompresses the fluid, which then travels to a condenser, which in turncools and condenses the fluid. The refrigerant then goes to an expansiondevice, which decreases the pressure of the fluid, and to theevaporator, where the fluid is vaporized, completing a refrigerationcycle.

Many refrigerant compressors are centrifugal compressors and have anelectric motor that drives at least one impeller to compressrefrigerant. The fluid is then directed downstream for use in thechiller system. Known refrigerant compressors have seals.

SUMMARY

In some aspects, the techniques described herein relate to a refrigerantcompressor, including: a stator; a rotor configured to rotate withrespect to the stator; and at least one step seal between the rotor andthe stator, wherein the step seal includes a first tooth and a secondtooth extending from the rotor toward the stator, wherein a downstreamsurface of the first tooth and an upstream surface of the second toothare arranged at an angle relative to one another, wherein the angle isless than 90°.

In some aspects, the techniques described herein relate to a refrigerantcompressor as recited claim 1, wherein the first tooth and the secondtooth include a pair of teeth, and the step seal includes a plurality ofpairs of teeth, and wherein each pair of teeth is provided in a steppedarrangement.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein the first and second teeth are formed in the rotorand an axial tooth is formed in the stator, and wherein the axial toothextends in a substantially axial direction radially outward of the firstand second teeth.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein the first tooth has a first point and the secondtooth has a second point, and wherein the first and second points arearranged at a common radial position.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein the downstream surface and the upstream surface meetat a curved surface to form a curved cavity.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein a radially inner cavity wall is arranged downstreamof the second tooth to form a second cavity downstream of the curvedcavity.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein the second cavity is a curved cavity.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein the second cavity is a square cavity.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein the stator has an abradable portion, and wherein thefirst and second teeth extend toward the abradable portion.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein the first and second teeth are configured to contactthe abradable portion and carve tracks into the abradable portion overtime.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein the refrigerant compressor is used in a heating,ventilation, and air conditioning (HVAC) chiller system.

In some aspects, the techniques described herein relate to a refrigerantcompressor, wherein a stator cavity is arranged in the stator, thestator cavity is arranged axially between the first tooth and the secondtooth.

In some aspects, the techniques described herein relate to arefrigeration system, including: a condenser; an evaporator; anexpansion device; and a compressor, wherein the compressor includes astator, a rotor configured to rotate with respect to the stator, and atleast one step seal between the rotor and the stator, wherein the stepseal includes a first tooth and a second tooth extending from the rotortoward the stator, wherein a downstream surface of the first tooth andan upstream surface of the second tooth are arranged at an anglerelative to one another, wherein the angle is less than 90°.

In some aspects, the techniques described herein relate to arefrigeration system as recited claim 13, wherein the first tooth andthe second tooth include a pair of teeth, and the step seal includes aplurality of pairs of teeth, each pair of teeth provided in a steppedarrangement.

In some aspects, the techniques described herein relate to arefrigeration system, wherein the first tooth has a first point and thesecond tooth has a second point, and wherein the first and second pointsare arranged at a common radial position.

In some aspects, the techniques described herein relate to arefrigeration system, wherein the downstream surface and the upstreamsurface meet at a curved surface to form a curved cavity.

In some aspects, the techniques described herein relate to arefrigeration system, wherein a radially inner cavity wall is arrangeddownstream of the second tooth to form a second cavity downstream of thecurved cavity.

In some aspects, the techniques described herein relate to arefrigeration system, wherein the second cavity is a curved cavity.

In some aspects, the techniques described herein relate to arefrigeration system, wherein the second cavity is a square cavity.

In some aspects, the techniques described herein relate to arefrigeration system, wherein the stator has an abradable portion,wherein the first and second teeth extend toward the abradable portion,and wherein the first and second teeth are configured to contact theabradable portion and carve tracks into the abradable portion over time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a refrigerant loop.

FIG. 2 shows a schematic view of a refrigerant compressor.

FIG. 3 shows a schematic view of an example step seal arrangement.

FIG. 4A shows an example step seal arrangement.

FIG. 4B shows the example step seal arrangement of FIG. 4A.

FIG. 5A shows another example step seal arrangement.

FIG. 5B shows the example step seal arrangement of FIG. 5A.

FIG. 6A shows another example step seal arrangement.

FIG. 6B shows the example step seal arrangement of FIG. 6A.

FIG. 7 shows a schematic view of another example step seal arrangement.

FIG. 8A shows an example step seal arrangement.

FIG. 8B shows the example step seal arrangement of FIG. 8A.

DETAILED DESCRIPTION

FIG. 1 illustrates a refrigerant system, which includes a compressor 10,a condenser 11, an evaporator 13, and an expansion device 15 arranged ina main refrigerant loop, or circuit, 17. This refrigerant system may beused in a chiller, for example. In that example, a cooling tower may bein fluid communication with the condenser 11. While a particular exampleof the refrigerant system is shown, this application extends to otherrefrigerant system configurations, including configurations that do notinclude a chiller. For instance, the main refrigerant loop 17 caninclude an economizer downstream of the condenser 11 and upstream of theexpansion device 15. The refrigerant system may be part of a heating,ventilation, and air conditioning (HVAC) chiller system, for example.

FIG. 2 illustrates a portion of the compressor 10 from FIG. 1 in moredetail, which in this example is a refrigerant compressor 10(“compressor 10”). The compressor 10 includes a housing 12, whichencloses an electric motor 14. The housing 12 may comprise one or morepieces. The electric motor 14 rotationally drives at least one impellerabout an axis A to compress refrigerant. Example refrigerants includechemical refrigerants, such as R-134a and the like. The motor 14 may bedriven by a variable frequency drive. The compressor 10 includes a firstimpeller 16 and a second impeller 18, each of which is connected to themotor 14 via a shaft 19. In the illustrated example, the impellers 16,18 are centrifugal impellers. While two impellers are illustrated, thisdisclosure extends to compressors having one or more impellers. In someembodiments, the compressor 10 may have two axial compression stages, ormay have a mixed stage (i.e., a stage with a radial and an axialcomponent) and an axial compression stage.

The housing 12 establishes a main refrigerant flow path F. Inparticular, the housing 12 establishes an outer boundary for the mainrefrigerant flow path F. A first, or main, flow of refrigerant isconfigured to flow along the main refrigerant flow path F between acompressor inlet 20 and a compressor outlet 22. In the illustratedexample, there are no inlet guide vanes disposed at the compressor inlet20. The lack of inlet guide vanes reduces the number of mechanical partsin the compressor 10. In other examples, inlet guide vanes may bearranged near the inlet 20.

From left to right in FIG. 2 , the main refrigerant flow path F beginsat the compressor inlet 20, where refrigerant is drawn toward the firstimpeller 16. The first impeller 16 is provided in the main refrigerantflow path F, and is arranged upstream of the second impeller 18 relativeto the main refrigerant flow path F. The first impeller 16 includes aninlet 161 arranged axially, generally parallel to the axis A, and anoutlet 160 arranged radially, generally perpendicular to the axis A.

Immediately downstream of the outlet 160, in this example, is a firstvaned diffuser 24. The main refrigerant flow path F extends through thediffuser 24 in a direction generally radially away from the axis A.Next, the main refrigerant flow path F turns 180 degrees in a cross-overbend 25, and flows radially inward through a return channel 27 towardthe second impeller 18. Like the first impeller 16, the second impeller18 includes an axially oriented inlet 181 and a radially oriented outlet180.

The compressor 10 has a plurality of seals 30A-30F. The seals 30A-30Fprevent the main refrigerant from escaping the flow path F. The seal 30Ais located between an outer diameter of the first impeller 16 and thehousing 12, near the inlet 161. The seal 30B is located between theshaft 19 and the housing 12 between the first and second impellers 16,18. The seal 30C is located between an outer diameter of the secondimpeller 18 and the housing 12, near the inlet 181. The seal 30D islocated at an inner diameter of the second impeller 18 and the motor 14.At least one of the seals 30A-30D is a step seal. In one particularembodiment, all of seals 30A-30D are step seals.

Step seals are used in turbomachinery to restrict or prevent the flow offluids, such as liquid or gas, between adjacent internal compartmentswith different pressures. A step seal prevents fluid flow fromtravelling from a higher pressure location to a lower pressure location.Step seals may generally include a plurality of fins or teeth thatdefine a plurality of cavities. The cavities entrap working fluidbetween a moving component and a stationary component. The trapped fluidthus creates a barrier that isolates a high pressure region within themachine from a region of lower pressure. In one example, the stationaryand moving components are a stator and a rotor, such as an impeller. Inanother example, the stationary component may be provided by an insertwithin the compressor housing.

FIG. 3 schematically shows an example stepped seal 30, which isrepresentative of any one of the seals 30A-30D. A seal flow path 32 isformed between a stator 38 and a rotor 40. In the illustratedembodiment, a plurality of teeth 42 extend generally radially outward(i.e., in a direction normal to axis A) from the rotor 40 in a directiontowards the stator 38 to define a plurality of cavities 48, 50 along theflow path 32 between the teeth 42. In another embodiment, a plurality ofteeth 42 extend outward from the stator 38.

The teeth 42 on the rotor 40 are arranged in a stepped arrangement,meaning some are arranged at a different radial position than others. Inparticular, in FIG. 3 , the teeth 42 are spaced-apart radially by steps44A. In the illustrated example, the steps 44A are formed such that theteeth are arranged in pairs 60. Each pair 60 has a first tooth 42A and asecond tooth 42B. The teeth 42A, 42B in each pair 60 are at the sameposition in a radial direction relative to an axis of rotation of therotor 40 (i.e., the axis A). The steps 44A and teeth 42 are cut out ofthe rotor 40 using known manufacturing techniques, in an example Similarsteps 44B are also cut into the stator 38 to align with the rotor 40.The steps 44B may be formed from an insert within the housing, forexample. The insert may be metallic. In the illustrated example, thereare seven of each of the steps 44A, 44B. In other examples, there may beat least five of each of the steps 44A, 44B. In a further example, theremay be ten or fewer of each step 44A, 44B. The teeth 42 and the steps44A, 44B introduce reverse flow, which stalls refrigerant flow (such astrapping flow in the cavities 48, 50), and helps decrease total leakage.

FIG. 4A illustrates further details of the step seal 30. The pairs 60 ofteeth 42A, 42B form two differently shaped cavities 48, 50. The cavities50 have a squared shape, while the cavities 48 have a rounded shape. Thefirst tooth 42A has an upstream surface 62 and a downstream surface 64.The second tooth 42B has an upstream surface 66 and a downstream surface68. In this example, the upstream surface 62 of the first tooth 42A andthe downstream surface 68 of a second tooth 42B form the walls of eachcavity 50. The cavity 50 has a radially inner cavity wall 51. The cavitywall 51 is substantially parallel to the axis A. The upstream surface 62and downstream surface 68 each extend radially outward from the cavitywall 51 at approximately a right angle. In other words, the cavity 50has a square-shaped bottom.

The downstream surface 64 of the tooth 42A and upstream surface 66 ofthe tooth 42B are angled at an angle with respect to the radialdirection. The surfaces 64, 66 are joined at a curved inner wall 47 toform the cavity 48. The cavity 48 is a curved cavity, while the cavity50 is a square cavity. The surfaces 64, 66 are arranged at an angle ⊖with respect to one another. The angle ⊖ is less than 90°. In a furtherexample, the angle ⊖ is between 45° and 90°.

The upstream surface 62 and downstream surface 64 of the first tooth 42Ameet at a point 72A. The upstream surface 66 and the downstream surface68 of the second tooth 42B meet at a point 72B. The points 72A, 72B arethe radially outermost portion of the rotor 40 in each step. In thisexample, the points 72A, 72B within each pair 60 extend to a sameposition in the radial direction. A radial clearance 80 is definedbetween the points 72A, 72B and the stator 38. In an example, the radialclearance 80 is at least 0.15 mm. An axial clearance 82 is definedbetween the downstream surface 68 of the second tooth 42B and theupstream surface 62 of an adjacent pair of teeth 60. In an example, theaxial clearance is at least 0.7 mm. An axially extending tooth 70extends in a substantially axial direction from the stator 38. The axialtooth 70 extends into the flowpath from the step 44B. The axial tooth 70may have an inner surface 74 and an outer surface 76. In one example,the inner surface 74 is substantially parallel to the axis of rotationA. The inner and outer surfaces 74, 76 are arranged at an angle ψ withrespect to one another. The angle ψ is less than 60°, for example. Theinner and outer surfaces 74, 76 extend in an upstream direction and meetat a point 78. In one example, the point 78 is aligned with the point72A in the axial direction.

FIG. 4B illustrates the fluid flow through the step seal 30. As shown,the radial teeth 42 and axial teeth 70 create eddies in the fluid,trapping fluid in the cavities 48, 50. Although an example seal 30 isshown, the particular shape and size may be tailored to a particularcompressor size, speed, and refrigerant. The cavities 48, 50 providerecirculation zones within the refrigerant leakage path to help decreaseleakage. The three sharp teeth 42A, 42B, 70 create vortices 90, 92, 94in the flow field. This tooth arrangement provides three recirculatingregions 91, 93, 95 per step to help passively control the flow,decreasing total leakage and increasing efficiency.

FIG. 5A illustrates another example step seal 130. To the extent nototherwise described or shown, the step seal 130 corresponds to the stepseal 30 of FIGS. 3, 4A, and 4B, with like parts having referencenumerals preappended with a “1.” In this example, the two teeth 142A,142B in each pair 160 form two angled cavities 148, 150. The upstreamsurface 162 of the first tooth 142A extends from the radially innercavity wall 151 at an angle α that is less than 90°. The downstreamsurface 168 of the second tooth 142B extends from the cavity wall 151 atsubstantially a right angle, or perpendicular to the axis A. Thus, thecavity 150 formed between adjacent pairs of teeth 60 has an angledshape. The downstream surface 164 of the first tooth 142A and theupstream surface 166 of the second tooth 142B meet at a point definingan angle ⊖. The angle ⊖ may be less than 90°, for example.

The upstream surface 162 and downstream surface 164 of the first tooth142A meet at a point 172A. The upstream surface 166 and the downstreamsurface 168 of the second tooth 142B meet at a point 172B. The points172A, 172B within each pair 160 extend to a same position in the radialdirection. In other words, the points 172A, 172B touch the locus of theradial clearance between the rotor 140 and the stator 138.

An axially extending tooth 170 extends in a substantially axialdirection from the stator 138. The axial tooth 170 extends into theflowpath from the step 144B. The inner surface 74 of the axial tooth 170is substantially parallel to the axis of rotation A. The inner and outersurfaces 174, 176 of the axial tooth 170 are arranged at an angle ψ withrespect to one another. The angle ψ is less than 60°, for example. Theinner and outer surfaces 174, 176 extend in an upstream direction andmeet at a point 178. In one example, the point 178 extends upstream ofthe first tooth 142A. In another example, the point 178 is substantiallyaligned with the first tooth 142A in the axial direction.

FIG. 5B illustrates the fluid flow through the step seal 130. This tootharrangement provides three recirculation zones 191, 193, 195 per step.The three sharp teeth 142A, 142B, 170 create vortices 190, 192, 194 inthe flow field. In some examples, this arrangement passively controlsthe flow to decrease total leakage, and may reduce leakage by 40-80%compared to known conventional seals.

FIG. 6A illustrates another example step seal 230. To the extent nototherwise described or shown, the step seal 230 corresponds to the stepseal 30 of FIGS. 3, 4A, and 4B, with like parts having referencenumerals preappended with a “2.” In this example, the step seal 230reduces leakage flow by using a stepped arrangement and using abradablematerials in the step seal. The performance of the seal 230 depends onthe stepped design and the radial clearance at the tips of the teeth242. In some known step seals, it can be difficult to control the amountof radial clearance, because thermal gradients, centrifugal and gaspressure forces, and shaft flexing, among other things may causedeflections between the components. The stator 238 includes an abradableportion 246 that is formed from an abradable material. In some examples,the abradable portion 246 is an insert arranged within a compressorhousing. The abradable portion 246 helps to minimize clearance betweenthe tips of the teeth 242 and the stator 238. The abradable portion 246starts off at a very close clearance to the rotor 240 and teeth 242 andgradually wears away over time as the teeth 242 come into contact withthe abradable portion 246.

As shown in FIG. 6A, the abradable portion 246 wears away as thecompressor 10 runs over time. A track 249 is carved into the abradableportion 246 radially outward of each of the teeth 242. Each of the teeth242 has a flat tip 272 that forms the track 249. As the rotor 240rotates, the teeth 242 contact the abradable portion 246 and wear offsome of the abradable portion 246 in the tracks 249 where the teeth 242contacted the abradable portion 246. The tracks 249 provide a very smallgap between the teeth 242 and the stator 238. In other words, once thetracks 249 are formed by the teeth 242, a portion 253 of the abradablematerial extends radially inward of the tracks 249 between tracks 249.The tracks 249 may be wider in the axial direction than the tips 272 ofthe teeth 242 due to axial movement of the impeller 16, 18.

In this arrangement, the upstream surface 262 of the first tooth 242Aand the downstream surface 268 of the second tooth 242B aresubstantially perpendicular to the radially inner cavity wall 251. Thesurfaces 262, 268 meet the cavity wall 251 at a rounded edge to form acurved cavity 250. The downstream surface 264 of the first tooth 242Ameets the upstream surface 266 of the second tooth 242B at a curvedsurface 247 to form a second curved cavity 248. The surfaces 264, 266are arranged at an angle ⊖ to one another. The angle ⊖ may be less than90° in one example. In a further example, the angle ⊖ is between 45° and90°. The particular tooth arrangement may be selected based on theparticular compressor size and speed, for example.

The abradable portion 246 is formed from an abradable material. Exampleabradable materials may include polytetrafluoroethylene (“PTFE”),polyamide, and other low strength alloys. The rotor 240 and teeth 242are generally formed from a hard material that can wear away theabradable portion 246, such as an aluminum alloy, stainless steel,carbon steel, nickel alloy (such as Inconel), etc. The abradable portion246 and the tracks 249 formed over time permit a minimal gap size, whichmakes it more difficult for the flow to continue, and thus improves thesealing capability of the seal 230.

The use of abradable materials may result in debris as the abradableportion is worn down. Although the abraded amount may be small, thesystem may include high precision parts. For example, bearings, sensors,and power electronics within the system cannot have intrusion of debris.In some examples, a debris trap may be arranged downstream of the teeth242 to capture any debris from the abradable portion 246 as it is wornaway. The debris trap may be arranged on a discharge path to redirectthe debris away from any sensitive components downstream of the seal230.

FIG. 6B illustrates the fluid flow through the step seal 230. Theabradable material may provide a significantly smaller radial clearancethan an arrangement with a hard material, which may further reduceleakage. The combination of two teeth 242A, 242B followed by a roundedrectangular cavity 250 provides a particular flow pattern having twovortices 290, 294 and two recirculation regions 291, 295. Thisrecirculation arrangement may decrease total leakage flow. In someexamples, this arrangement passively controls the flow to decrease totalleakage, and may reduce leakage by 40-80% compared to known conventionalseals.

FIG. 7 illustrates another example step seal 330. To the extent nototherwise described or shown, the step seal 330 corresponds to the stepseal 30 of FIGS. 3, 4A, and 4B, with like parts having referencenumerals preappended with a “3.” In this example, the teeth 342 on therotor 340 are spaced-apart radially by steps 344A. In the illustratedexample, the steps 344A are formed such that the teeth are arranged inpairs 360. Each pair 360 has a first tooth 342A and a second tooth 342B.The teeth 342A, 342B in each pair 360 are at the same position in aradial direction relative to an axis of rotation of the rotor 340 (i.e.,the axis A). Cavities 350 are formed between each pair of teeth 360, andcavities 348 are formed between the teeth 342A, 342B within each pair360.

The steps 344A, teeth 342, and cavities 350 are cut out of the rotor 40using known manufacturing techniques. Similar steps 344B are also cutinto the stator 338 to align with the rotor 340. In this example,cavities 371 are formed in the stator 338 between the steps 344B. Insome examples, the cavity 371 forms a tooth 359 in the stator 338 thatextends towards the rotor 340. The tooth 359 may be have a substantiallysimilar size and shape as the tooth 342A. The teeth 342, 359 and thesteps 344A, 344B introduce reverse flow, which stalls refrigerant flow(such as trapping flow in the cavities 348, 350, 371), and helpsdecrease total leakage.

FIG. 8A illustrates the example step seal arrangement of FIG. 7 . Inthis example, the two teeth 342A, 342B in each pair 360 form twocavities 348, 350. The cavity 350 is formed between an upstream surface362 of the first tooth and a downstream surface 368 of the second tooth342B. In this example, the cavity wall 351 is rounded at a radiallyinnermost portion. The cavity wall 351 may have a semi-circle or radius,for example. A wall 355 opposite the rounded end of the cavity wall 351may be substantially parallel to the axis A, for example. The cavity 350has a rectangular shape with a rounded end, for example. The surfaces362, 368 may extend substantially perpendicular relative to the axis A.The tooth 359 may meet the wall 355 at a fillet 357, in some examples.

The cavity 348 formed between the teeth 342A, 342B within a pair ofteeth 360 has an angled shape. The downstream surface 364 of the firsttooth 342A and the upstream surface 366 of the second tooth 342B areangled relative to the axis A. The downstream surface 364 of the firsttooth 342A and the upstream surface 366 of the second tooth 342B arearranged at an angle ⊖ relative to one another. The angle ⊖ may be about90°, for example. In other examples, the angle ⊖ may be less than 90°. Acavity 371 is formed in the stator 338 opposite the cavity 348. Thecavity 371 may have a similar shape as the cavity 348 and besubstantially aligned with the cavity 348. The cavity 371 is areflection of the cavity 348 about a plane parallel to the axialdirection and arranged radially between the cavities 348, 371, in oneexample.

The upstream surface 362 and downstream surface 364 of the first tooth342A meet at an end surface 372A. The upstream surface 366 and thedownstream surface 368 of the second tooth 342B meet at an end surface372B. The end surfaces 372A, 372B within each pair 360 extend to a sameposition in the radial direction. The geometry of the flow path changesthe speed and trajectory of fluid flow, which may decrease leaks throughthe seal.

FIG. 8B illustrates the fluid flow through the step seal 330. As fluidflows from left to right in this example, the tooth and cavityarrangement provides three recirculation zones 391, 393, 395 per step.The arrangement of teeth 342 and cavities 348, 350, 371 create vortices390, 392, 394 in the flow field. In some examples, this arrangementpassively controls the flow to decrease total leakage.

Any of the above described step seals 30, 130, 230, 330 may be used inany of the seal locations 30A-30D. In some examples, different types ofstep seals 30, 130, 230, 330 may be used in different seal locations30A-30D within the same compressor 10.

Although the different examples have the specific components shown inthe illustrations, embodiments of this disclosure are not limited tothose particular combinations. It is possible to use some of thecomponents or features from one of the examples in combination withfeatures or components from another one of the examples. In addition,the various figures accompanying this disclosure are not necessarily toscale, and some features may be exaggerated or minimized to show certaindetails of a particular component or arrangement.

One of ordinary skill in this art would understand that theabove-described embodiments are exemplary and non-limiting. That is,modifications of this disclosure would come within the scope of theclaims. Accordingly, the following claims should be studied to determinetheir true scope and content.

1. A refrigerant compressor, comprising: a stator; a rotor configured torotate with respect to the stator; and at least one step seal betweenthe rotor and the stator, wherein the step seal comprises a first toothand a second tooth extending from the rotor toward the stator, wherein adownstream surface of the first tooth and an upstream surface of thesecond tooth are arranged at an angle relative to one another, whereinthe angle is less than 90°.
 2. The refrigerant compressor as recitedclaim 1, wherein the first tooth and the second tooth comprise a pair ofteeth, and the step seal comprises a plurality of pairs of teeth, andwherein each pair of teeth is provided in a stepped arrangement.
 3. Therefrigerant compressor as recited in claim 1, wherein the first andsecond teeth are formed in the rotor and an axial tooth is formed in thestator, and wherein the axial tooth extends in a substantially axialdirection radially outward of the first and second teeth.
 4. Therefrigerant compressor as recited in claim 1, wherein the first toothhas a first point and the second tooth has a second point, and whereinthe first and second points are arranged at a common radial position. 5.The refrigerant compressor as recited in claim 1, wherein the downstreamsurface and the upstream surface meet at a curved surface to form acurved cavity.
 6. The refrigerant compressor as recited in claim 5,wherein a radially inner cavity wall is arranged downstream of thesecond tooth to form a second cavity downstream of the curved cavity. 7.The refrigerant compressor as recited in claim 6, wherein the secondcavity is a curved cavity.
 8. The refrigerant compressor as recited inclaim 6, wherein the second cavity is a square cavity.
 9. Therefrigerant compressor as recited in claim 1, wherein the stator has anabradable portion, and wherein the first and second teeth extend towardthe abradable portion.
 10. The refrigerant compressor as recited inclaim 9, wherein the first and second teeth are configured to contactthe abradable portion and carve tracks into the abradable portion overtime.
 11. The refrigerant compressor as recited in claim 1, wherein therefrigerant compressor is used in a heating, ventilation, and airconditioning (HVAC) chiller system.
 12. The refrigerant compressor asrecited in claim 1, wherein a stator cavity is arranged in the stator,the stator cavity is arranged axially between the first tooth and thesecond tooth.
 13. A refrigeration system, comprising: a condenser; anevaporator; an expansion device; and a compressor, wherein thecompressor includes a stator, a rotor configured to rotate with respectto the stator, and at least one step seal between the rotor and thestator, wherein the step seal comprises a first tooth and a second toothextending from the rotor toward the stator, wherein a downstream surfaceof the first tooth and an upstream surface of the second tooth arearranged at an angle relative to one another, wherein the angle is lessthan 90°.
 14. The refrigeration system as recited in claim 13, whereinan axial tooth is formed in the stator, and wherein the axial toothextends in a substantially axial direction radially outward of the firstand second teeth.
 15. The refrigeration system as recited claim 13,wherein the first tooth and the second tooth comprise a pair of teeth,and the step seal comprises a plurality of pairs of teeth, each pair ofteeth provided in a stepped arrangement.
 16. The refrigeration system asrecited in claim 13, wherein the first tooth has a first point and thesecond tooth has a second point, and wherein the first and second pointsare arranged at a common radial position.
 17. The refrigeration systemas recited in claim 13, wherein the downstream surface and the upstreamsurface meet at a curved surface to form a curved cavity.
 18. Therefrigeration system as recited in claim 16, wherein a radially innercavity wall is arranged downstream of the second tooth to form a secondcavity downstream of the curved cavity.
 19. The refrigeration system asrecited in claim 17, wherein the second cavity is a curved or squarecavity.
 20. The refrigeration system as recited in claim 13, wherein thestator has an abradable portion, wherein the first and second teethextend toward the abradable portion, and wherein the first and secondteeth are configured to contact the abradable portion and carve tracksinto the abradable portion over time.